A polyolefin resin is excellent in moldability, rigidity, heat resistance, chemical resistance, electrical insulation properties, and the like, and is inexpensive, so that it is widely used for general purposes as a film, fiber, and other molded products with various shapes. On the other hand, the polyolefin resin is a high-molecular substance that has no polar group in its molecule, so-called non-polar, and that is very inert. Further, the polyolefin resin has high crystallinity and significantly low solubility in solvents, and therefore has problems in adhesiveness, coatability, and the like. Also, the polyolefin resin repels water due to poor wettability for water, and therefore has the problem that an aqueous coating material cannot be applied thereon, and the like.
Conventionally, as a method for improving wettability, there are known a method of subjecting the surface of a thermoplastic resin substrate, for example, a polyolefin resin molded product to corona treatment or plasma treatment (e.g., see Patent Document 1), a method of adding a surfactant to a polyolefin resin composition to form a molded product (e.g., see Patent Document 2), and the like.